Histogramming
Histogramming is a process of turning ROOT trees into 1D/2D histograms. You can apply histogramming to your input samples or samples that already pass some skimming (could be multiple levels of skimming).
If you want to generate histograms of branches that already exist in your input tree, have a look at My first histogrammer tutorial.
When this is not enough and you want to create some custom variables + perhaps apply some cuts on-the-fly, you should refer to the Custom histogrammer tutorial page.